The present invention generally relates to reclosable plastic bags and, more particularly, to a slider-operated fastener with spaced notches and associated preseals.
In one method of making reclosable plastic bags, a continuous fastener is sealed to a moving web of thermoplastic film. To form individual bags, the web is folded along a fold parallel to the direction of web movement, and the folded web is sealed at bag-width distances apart along side seals that are generally transverse to the direction of web movement. To facilitate opening and closing the fastener, sliders are preferably applied to the fastener at bag-width distances apart.
The fastener includes a pair of interlocking profiles and a pair of fins/flanges extending downward from the respective profiles. In one technique for installing sliders on the fastener, notches are formed in the fastener at bag-width distances apart. The side seals, which are formed later in the bag manufacturing process, are aligned with the respective notches. To install a slider on the fastener via a respective notch, the slider is first positioned within the notch while the web is temporarily stopped, and then the slider is threaded onto an end of the fastener in response to relative movement of the slider and fastener. This installation technique is disclosed in U.S. patent application Ser. No. 09/307,937 (PCOS015) entitled xe2x80x9cZipper and Zipper Arrangements and Methods of Manufacturing the Samexe2x80x9d, filed May 10, 1999, and incorporated herein by reference in its entirety.
To form a notch, a short segment of the interlocked profiles and an upper portion of the fins extending from that segment are cut away from the fastener, leaving only a lower portion of the fins bridging opposite sides of the notch. Due to the removal of most of the fastener at the notches, the fastener can be difficult to control during such downstream operations as slider installation and when tensioned by various rollers in a bag making machine. The fastener tends to twist and distort and the fastener profiles tend to shift longitudinally relative to each other. In addition, the notches produce areas where air or liquid can potentially leak into or out of the bags eventually formed by the bag making machine.
To overcome the aforementioned shortcomings, the present invention provides a unique slider-operated fastener and method of making the same. The slider-operated fastener comprises first and second opposing tracks including respective first and second interlocking profiles and respective first and second fins extending downward from the respective first and second profiles. The first and second fins are sealed to each other by a plurality of spaced preseals. After generating each preseal, a notch is formed in the profiles and upper portions of the fins at the generated preseal. To install a slider onto the fastener, the slider is initially positioned within the respective notch and then threaded onto the fastener in response to relative movement of the slider and the fastener. Either before or after the steps of forming each preseal and respective notch and installing the respective slider, the fastener is attached to a moving web of plastic film. The fastener-carrying web is later folded and sealed to form individual plastic bags.
The preseals are advantageous in that they allow the fastener to be controlled during such downstream operations as notch formation and slider installation and when the fastener is tensioned by various rollers in the bag making machine. The preseals keep the interlocked profiles together and prevent them from moving longitudinally relative to each other. In addition, the preseals generally encompass the respective notches to assist in providing a leakproof barrier to entry into an interior of the fastener between the fins via the notches. This leakproof barrier is effective in the ultimately formed plastic bags.